1. Field of the Invention
The present invention relates to a continuous sheet having optical functions and, more particularly, to a continuous plastic sheet having optical functions such as (light) transmission, refraction, reflection, scattering, interference, polarization and the like, i.e., plastic lens, light reflection sheets, prism sheets, anti-dazzling sheets, diffusion sheets and a combination of such optical effects, which have been imparted by a continuous release sheet having a desired three-dimensional pattern in its surface.
2. Description of the Prior Art
Nowadays, films or sheets utilizing the optical properties of synthetic resin films or sheets (both called "sheet" hereinafter unless otherwise noted) are deeply related with industrial and daily living activities. Most of them, however, have their surface flat, competing merely in transparency of resins, or control ray transmissivity by such as making the surface matte or adding additives.
Lately, plastic lenses, and optically functional sheets such as prism sheets, anti-dazzling sheets and diffusion sheets as a structural component of liquid crystal displays used for note-type personal computers or liquid crystal TVs, which have special surface structures for adjusting, among others, surface reflectivity, refraction, scattering or combinations thereof have been drawing particular attention.
A sheet with a specific three-dimensional pattern is often made by press molding by the use of an embossed plate having a desired particular three-dimensional pattern or by injection molding. However, these methods are either poor in producibility because of a batch type production or have a problem of not being suitable for the formation of thin sheets. Meanwhile, for the production of a continuous sheet having a three-dimensional pattern, there are such alternatives as extruding through a profile die or using a proper embossing roll for patterning the surface of a sheet, but with these methods it is difficult to impart to the sheet surface a precise pattern for imparting thereto an optical performance and, even if such effect should be attainable, it is only attained partly, thus being inaccurate.
Hence, for obtaining a continuous sheet with a precise three-dimensional pattern imparted thereto, there has been proposed in U.S. Pat. No. 4,244,683 a method in which a molten synthetic resin is flown onto a planar press mold clamped to a movable belt for continuous embossing. Even by this method, however, it is impossible to obtain a continuous sheet having a seamless three-dimensional pattern which enables a continuous optical function.
It is possible to produce a patterned continuous sheet by coating by a method of, for example, coating the sheet surface with minute particles. This method, however, has defects of some foreign matters being contained therein or of the patterns attainable being limited by the size of such minute particles. Moreover, surface patterns are attainable by a similar printing method, but it is incapable of forming a three-dimensional pattern with its precision being enough for attaining a desired optical performance.